1. Field of the Invention
This invention relates to resole resin systems for use in pultrusion processes having longer pot life and low free formaldehyde emission, pultrusion composites comprising a plurality of filaments bonded together by a resole resin having a resorcinol novolac hardener and pultrusion processes employing the novel resin system.
2. Description of the Related Art
"Pultrusion" is a well known term of art to describe the drawing of a plurality of fibrous reinforcement coated with a binding solution, through a die in order to shape the fibrous reinforcement and binder into a unitary article of desired shape.
Prior uses of fibrous reinforcement, such as glass fibers, have permitted the formation of varying shapes by the pultrusion process so as to provide a composite structural member which are typically stronger and lighter and may be less expensive than similarly sized single material members, such as wood, and thus, can be used as a competing product to conventional wood or metal structural materials. One particular product of interest is primarily for off-shore platforms, e.g. pultruded grate systems for ships and off-shore oil wells.
Tingley, U.S. Pat. No. 5,456,781, generally illustrates, in FIG. 3, a schematic for a pultrusion process in which a plurality of fiber rovings are pulled through a resin bath and then a forming die and subsequently through a heated die that cures the resin materials and shapes the rovings and resin. Preferred rate through the pultrusion apparatus is 3-5 feet/minutes (0.9-1.5 m/minute). Although glass fiber has been mentioned as the fiber filaments or rovings, other materials, including synthetic fibers, carbon fibers and inorganic fibers, e.g. ceramic fibers, can be used as the filaments or rovings. Suitable for use as fibers in tension are aramid fibers, which are commercially available from E.I. Dupont de Nemours & Company of Delaware under the trademark "KEVLAR" and high modulus polyethylene which is available under the trademark "Spectra" from Allied Fibers of Allied Signal, Petersburg, Va. Synthetic fibers preferably having a modulus of elasticity in tension that is relatively high. For example, synthetic fibers of KEVLAR.TM. have a modulus of elasticity and tension of about 18.times.10.sup.6 psi (124,000 MPa).
Suitable for use as compression fibers are carbon fibers such as commercially available carbon fibers which have a modulus of elasticity in compression in a range of about 34.times.10.sup.4 to 36 .times.10.sup.4 PSI (234,000-248,000 Mpa).
As suitable resin materials are mentioned epoxy, polyester, vinyl ester, phenolic resins, polyamides, or polystyrylpyridine (PSP) or thermoplastic resins, such as polyethylene terapthylate (PET) and nylon-66.
It is also been known to use a phenolic resin containing resorcinol, such as a commercially available phenolic resin containing about 0-60% resorcinol, which is commercially available under the trade designation RESORCIPHEN.RTM. 2074A-2026B now owned by Borden Chemical, Inc. of Columbus, Ohio.
These phenolic resins containing resorcinol are disclosed in the Dailey U.S. Pat. Nos. 5,075,413 and 5,075,414. The resorcinolic component is selected from resorcinol and resorcinol formaldehyde novolak resin. This is reacted with a phenolic resole resin which has a room temperature cure in as little as eight hours. In addition, a methylene donor may be employed in the reaction.
The entire subject matter of the aforementioned '781, '413 and '414 patents are herein incorporated by reference.
While such products according to the prior art do produce a resin bound composite of fibers, the difficulty with the prior art phenolic resin systems containing resorcinol is a short pot life (low stability) and high formaldehyde emission, which are a source of pollutants of the atmosphere.